The present invention pertains to catheter systems and, more particularly, to intraluminal catheter assemblies used in diagnostic and therapeutic applications.
Intraluminal catheter assemblies are employed to diagnose and/or treat abnormalities within the human vasculature. A typical intraluminal catheter assembly includes a distally mounted operative element, such as, e.g., an ablation electrode, which is in electrical communication with a proximally located operative element, such as, e.g., an RF generator. Currently, intraluminal catheter assemblies include elongate catheter bodies in which internal lumens are extruded for the purpose of routing transmission lines between the distally mounted operative element and the proximally located operative element.
Often, intraluminal catheter assemblies support multiple distally mounted operative elements, thereby providing the physician with a single multi-functional platform. Because the radius of the catheter body must be small enough to be transported through the vasculature, however, the size and number of internal lumens which can be extruded through the catheter body becomes a critical factor, thereby limiting the amount, combination and/or performance of distally mounted operative elements supported by these catheter assemblies.
For example, as shown in FIG. 12, a typical ultrasonic imaging/ablation catheter assembly 300 includes an elongate catheter body 302 with distally mounted ablation electrodes 304 and a distally disposed rotatable ultrasonic transducer 306 to allow a physician to more easily image and ablate abnormal vasculature tissue.
The ablation electrodes 304 are electrically coupled to a proximally disposed RF generator (not shown) via transmission lines 308, which are routed through a first internal lumen 310 extruded within the catheter body 302. Operation of the RF generator transmits radio frequency electrical energy through the transmission lines 308 to the ablation electrodes 304, which in turn emit RF energy into the vasculature tissue adjacent the ablation electrodes 304.
The ultrasonic transducer 306 is mounted in a transducer housing 312 disposed within the catheter body 302. The ultrasonic transducer 306 is mechanically and rotatably coupled to a proximally disposed drive unit (not shown) via a drive cable 314 rotatably disposed within a second extruded internal lumen 316. The ultrasonic transducer 306 is electrically coupled to a proximally disposed signal transceiver (not shown) via a transmission line (not shown) disposed within the drive cable 314. Operation of the drive unit rotates the drive cable 314, and thus the ultrasonic transducer 306, with respect to the catheter body 302. Simultaneous operation of the transceiver alternately transmits and receives electrical energy to and from the ultrasonic transducer 306 via the drive cable disposed transmission line, thereby providing the physician with 360xc2x0 imaging of the vasculature tissue adjacent the ultrasonic transducer 306.
The catheter assembly 300 is configured to allow the drive cable 314 and distally mounted ultrasonic transducer 306 to be xe2x80x9cback loadedxe2x80x9d (i.e., inserted or retracted) through the second interior lumen 316. The size of the ultrasonic transducer 306, and thus the integrity of the imaging data obtained therefrom, is thus limited by the size of the second interior lumen 316. The size of the second interior lumen 316, however, could be increased by eliminating the first interior lumen 308.
Another concern with respect to intraluminal catheter assemblies is the coupling of an electrical signal between a distal non-rotatable operative element and a proximal rotatable operative element, such as, e.g., the ultrasonic transducer 306 and transceiver employed in the catheter assembly 300 described above. Typically, to provide this inductive coupling, an inductive coupler is connected in parallel with the signal wires at the proximal end of the catheter. As such, that portion of the signal wires distal to the inductive coupler rotate with the transducer, and must therefore be installed within the entire length of the drive cable. Although a proximally disposed inductive coupler adequately provides inductive coupling between the transducer and the transceiver, this arrangement has several disadvantages.
For example, a signal wire disposed drive cable aggravates a phenomenon suffered by ultrasound imaging catheters called non-uniform rotational distortion (xe2x80x9cNURDxe2x80x9d). NURD is caused by frictional forces between the rotating imaging core and the inner wall of the catheter, which are magnified by the many twists and turns that a catheter must undergo so that the transducer can be positioned in the desired imaging location within the patient""s body. These frictional forces cause the imaging core to rotate about its axis in a non-uniform manner, thereby resulting in a distorted image.
NURD can be minimized by xe2x80x9coptimizingxe2x80x9d the construction of the drive cable, for example, by varying the drive cable""s diameter, weight, material, etc. The characteristics of the drive cable, however, are dictated in part by the signal wires disposed therein, thereby limiting this NURD-minimizing optimization. Further, the signal wires contribute non-uniformities to the drive cable that cannot be optimized.
A further disadvantage of a proximally disposed inductive coupler is that the diameter of the drive cable must be increased to accommodate the signal wires, thereby occupying space within the catheter that could otherwise be used to support other functions such as, e.g., pull-wire steerability, angioplasty balloon therapy, ablation therapy, or blood flow (Doppler) measurements.
A further disadvantage of a proximally disposed inductive coupler is that the remoteness of the coupler prevents usage thereof for transducer optimization, i.e., transducer tuning and matching or prevention of transducer low frequency mode emittance. Thus, additional measures must be employed to either optimize the transducer or to minimize the undesirable effects thereof.
For instance, at its normal frequency of operation, the transducer exhibits a net capacitive reactance. Thus, inductive reactance should be provided to xe2x80x9ccancelxe2x80x9d this capacitive reactance, so as to efficiently couple the transmit/receive signals to the transducer (e.g., to maximize signal-to-noise ratios). A proximally disposed inductive coupler does not provide the needed inductance, however, since the inductance producing structure must be placed along the signal wires in close proximity to the transducer. Instead, such a result can be accomplished by placing an inductive coil in series with the signal wires, as demonstrated in U.S. Pat. No. 4,899,757 issued to Pope, Jr. et al.
In addition to canceling the capacitive reactance produced by the transducer, it is also desirable to match the input impedance of the transducer with the characteristic impedance of the signal wires, so as to minimize signal reflection. In particular, a proximally disposed inductive coupler is by definition proximal to the signal wires and can therefore not be used to perform such matching. An attempt can be made to optimize the size and material of the transducer for matching of the signal wires therewith. Such optimization is limited, however, and to the extent any signal reflections are not eliminated, the signal power will accordingly be reduced.
Still further, an excited transducer naturally creates a low frequency mode of vibration that further produces multiples of higher frequency modes (e.g., 4 MHz, 8 MHz, 12 MHz, etc.). These unwanted signals cannot be eliminated through the use of a proximally disposed inductive coupler, but must be filtered out at the proximal end of the catheter. The signals within the frequency band in which the imaging system is to be operated cannot be filtered out, however, and must be dealt with as interference.
Theoretically, a parallel inductor can be placed in close proximity to the transducer to short out the low frequency mode, thereby eliminating the higher frequency modes. Such an arrangement, however, is complicated and expensive, and thus inefficient for the mere purpose of eliminating unwanted modes of transducer vibration.
Therefore, it would be desirable to increase the available space within a catheter body by eliminating or at least reducing the number of interior lumens that support transmission lines. It would be further desirable to improve the mechanical and electrical performance of a catheter that employs a distal rotatable operative element and a proximal non-rotatable operative element.
The present invention overcomes the afore-described drawbacks of conventional intraluminal catheter assemblies by providing improved intraluminal catheter assemblies that employ a distally disposed inductive coupling assembly and/or at least one conductor embedded in the exterior wall of an elongate catheter body to provide communication between respective distal and proximal operative elements.
In a first preferred embodiment, a catheter assembly according to the present invention includes an elongate catheter body having a proximal end and a distal end with a drive cable disposed therein and rotatable relative to the catheter body. A first electro-magnetic element is disposed proximate the distal end of the catheter body and in electrical communication with a proximal operative element proximate the proximal end of the catheter body. A second electromagnetic element is rotatably coupled to the drive cable and in electrical communication with a distal operative element rotatably coupled to the drive cable. The first and second electromagnetic elements form an inductive coupler.
In accordance with a further aspect of the present invention, the first electro-magnetic element comprises a stator fixably disposed in the catheter body, and the second electro-magnetic element comprises a rotor mounted to a distal end of the drive cable, wherein the stator comprises a generally hollow cylinder, and the rotor comprises a rod rotatably disposed in the hollow cylinder. The stator and rotor are preferably made of a ferrite material, with the stator having a first electrically conductive coil disposed on the inner surface of the hollow cylinder, and wherein the rotor having a second electrically conductive coil disposed on the outer surface of the rod.
The stator and rotor having opposing surface areas, wherein the respective stator and rotor surface areas, along with the respective diameter, size and number of turns of the first and second electrically conductive coils, are selected such that the value of the inductive reactance of the inductive coupler is substantially equal to the capacitive reactance of the operative element, which may be, e.g., an ultrasonic transducer.
In accordance with a still further aspect of the present invention, the catheter assembly includes a first conductor having a distal end electrically coupled to the stator and a proximal end configured for electrically coupling to a signal transceiver. Preferably, the first conductor is disposed within the catheter body, with the ratio of turns between the first and second electrically conductive coils being selected such that the input impedance looking into the inductive coupler from the transmission line substantially matches the characteristic impedance of the transmission line. The catheter assembly includes a second conductor having a proximal end electrically coupled to the rotor and a distal end electrically coupled to an ultrasonic transducer. The signal transceiver and ultrasonic transducer are configured to provide 360xc2x0 imaging of body tissue, such as, e.g., arterial tissue.
In a second preferred embodiment, a catheter assembly according to the present invention includes an elongate catheter body having a proximal end and a distal end with a drive cable disposed therein and rotatable relative to the catheter body. First and second electro-magnetic elements are disposed proximate the distal end of the catheter body and respectively in electrical communication with first and second proximal operative elements proximate the proximal end of the catheter body. Third and fourth electro-magnetic elements are rotatably coupled to the drive cable and in electrical communication with first and second distal operative elements rotatably coupled to the drive cable. The first and third electro-magnetic elements form a first inductive coupler, and the second and fourth electro-magnetic elements form a second inductive coupler.
In accordance with a further aspect of the present invention, the first and second electro-magnetic elements respectively comprise first and second stators fixably disposed in the catheter body, and the third and fourth electro-magnetic elements comprise first and second rotors mounted to a distal end of the drive cable, wherein the stators respectively comprise generally hollow cylinders, and the rotors respectively comprise rods rotatably disposed in the hollow cylinders, respectively.
In accordance with a still further aspect of the present invention, the catheter assembly includes first and second conductors having distal ends electrically coupled to the first and second stators, respectively, and proximal ends configured for electrically coupling to first and second signal transceivers, respectively. The catheter assembly includes third and fourth conductors having proximal ends electrically coupled to the first and second rotors, respectively, and distal ends electrically coupled to first and second ultrasonic transducers, respectively. The first signal transceiver and first ultrasonic transducer are configured to provide 360xc2x0 imaging of body tissue, such as, e.g., arterial tissue, and the second signal transceiver and second ultrasonic transducer are configured to provide Doppler measurements of the blood flow through a vessel, such as, e.g., an artery.
In a third preferred embodiment, a catheter assembly according to the present invention includes an elongate telescoping catheter body having a proximal end and a distal end with a drive cable disposed therein and rotatable relative to the catheter body. A first electro-magnetic element is disposed proximate the distal end of the catheter body and in electrical communication with a proximal operative element proximate the proximal end of the catheter body. A second electro-magnetic element is rotatably coupled to the drive cable and in electrical communication with a distal operative element rotatably coupled to the drive cable. The first and second electro-magnetic elements form an inductive coupler. The telescoping catheter body is movably disposed in a main catheter body to provide longitudinal displacement of the distal operative element relative to the main catheter body. The particular aspects of the third preferred embodiment are similar to those of the first preferred embodiment with the exception that the controlled longitudinal displacement of the telescoping catheter body relative to the main catheter body allows for longitudinally spaced 360xc2x0 image slices.
In a fourth preferred embodiment, a catheter assembly according to the present invention includes an elongate catheter body with a first distal operative element disposed thereon. The first distal operative element is electrically coupled to a first proximal operative element via a transmission line embedded in the wall of the catheter body. The catheter assembly includes a drive cable and a second distal operative element rotatably coupled to the drive cable. The second distal operative element is electrically coupled to a second proximal operative element via a transmission line within the drive cable.
In accordance with a further aspect of the invention, the first distal operative element comprises a first ultrasonic transducer mounted to the distal end of the catheter body, such that the face of the ultrasonic transducer is perpendicular to the axis of the catheter body. The second distal operative element comprises a second ultrasonic transducer mounted to the distal end of the drive cable. The first and second proximal elements respectively comprise signal transceivers. The first signal transceiver and first ultrasonic transducer are configured to provide Doppler measurements of the blood flow through a vessel, such as, e.g., an artery, and the second signal transceiver and second ultrasonic transducer are configured to provide 360xc2x0 imaging of body tissue, such as, e.g., arterial tissue. The catheter wall can be used as a portion of the transmission line.
In a fifth preferred embodiment, a catheter assembly according to the present invention includes an elongate catheter body with first and second distal operative elements disposed thereon. The first and second distal operative elements are electrically coupled to a first proximal operative element via respective first and second transmission lines embedded in the wall of the catheter body. The catheter assembly includes a drive cable and a third distal operative element rotatably coupled to the drive cable. The third distal operative element is electrically coupled to a second proximal operative element via a third transmission line within the drive cable.
In accordance with a further aspect of the invention, the first and second distal operative elements comprise respective first and second electrodes, such as, e.g., ablation electrodes, mounted to the distal end of the catheter body. The first proximal element comprises an RF generator. The third distal operative element comprises an ultrasonic transducer mounted to the distal end of the drive cable. The second proximal element comprises a signal transceiver. The first and second ablation elements and the RF generator are configured to provide ablation therapy to adjacent body tissue, such as, e.g., arterial tissue, and the ultrasonic transducer and signal transceiver are configured to provide 360xc2x0 imaging of body tissue, such as, e.g., arterial tissue.
In a sixth preferred embodiment, a catheter assembly according to the present invention includes an elongate catheter body with a plurality of distal operative elements disposed thereon. The plurality of distal operative elements are respectively electrically coupled to at least one proximal operative element via a plurality of transmission lines embedded in the wall of the catheter body.
In accordance with a further aspect of the invention, the plurality of distal operative elements comprise respective transducer elements, which are circumferentially arranged around the catheter body to form a phased array. The proximal element comprises a transceiver, which is configured to provide phased electrical signals to the plurality of transducer elements.
Other and further objects, features, aspects, and advantages of the present invention will become better understood with the following detailed description of the accompanying drawings.